I have experienced this with Levi jeans. I buy a nice pair of jeans, they fit well, look nice, affordable etc. I need more jeans, so I go to the store a month later and try on a bunch of different jeans. One pair says they are the same size but fit entirely different, so I chalk it up as being a different "fit" of jeans. Nope, when I get home, they were an IDENTICAL pair, but fit like a different size.

I once talked to someone from the jeans industry and he attributed this phenomenon to brands switching between different manufacturers for their fabrics. So thismanufacturer A might produce the fabric at a weight of XX g/m² and, next year, manufacturer B might produce it at YY g/m². XX and YY will be close but often not exactly the same and this will affect the fit.